KR20020011057A - Method for manufacturing microporous poly(vinylchloride) membrane and microporous poly(vinylchloride) manufactured thereby - Google Patents

Abstract

PURPOSE: A process for manufacturing a microporous polyvinylchloride membrane via solvent induced phase separation(SIPS) is provided to control pore morphology such as pore size and porosity to be suitable for microfiltration, where especially the flux of pure water is improved as nonsolvent concentration increase, and further in the case that the nonsolvent is either n-propyl alcohol or n-butyl alcohol, the flux of pure water is improved as relative humidity increase within relative humidity range 50 to 90%. CONSTITUTION: The process for microporous polyvinylchloride membrane includes: dissolution of polyvinylchloride into tetrahydrofuran(THF) solution; addition of 1-40wt.% of an alcohol selected from n-propyl alcohol or n-butyl alcohol, which is miscible with the tetrahydrofuran(THF) while acting as a nonsolvent to the polyvinylchloride; coating non-woven polyester fabric with a mixed solution obtained in 2nd step; drying at 25deg.C under the atmosphere of relative humidity of 50 to 90%. The microporous polyvinylchloride membrane has overall porosity of 25-80%, pore size distribution within range of 0.01 to 2μm and it has a net flux of 25 to 7000LMH.

Description

Method for manufacturing microporous polyvinyl chloride membrane and microporous polyvinyl chloride membrane produced by the same methodMethod for manufacturing microporous poly (vinylchloride) membrane and microporous poly (vinylchloride) manufactured according}

The present invention relates to a method for producing a porous membrane used for filtration and the like. More specifically, in the production of porous membranes using a phase separation method, the introduction of a non-solvent additive in a polymer solution improves the permeability of pure water, and the porosity and pore size of the membrane can be controlled. The higher the content, the greater the effect. Also, in the case of the non-solvent n-propyl alcohol and n-butyl alcohol, the relative humidity increased in the range of 50-90% relative humidity, the better the permeation performance of pure water. Reached.

The process for preparing a porous membrane includes a non-solvent induced phase separation process and a phase separation process according to a wet and dry method. However, from the thermodynamic viewpoint of the polymer solution, the membrane forming mechanisms according to the above processes are characterized in that the nucleus-growth (NG) mechanism in the metastable region located between the binodal and the spinodal and the phase separation in the unstable region inside the spinodal (P. van de Witte et al., Journal of Membrane Science, 117 (1996) 1-31) In general, in order to improve the permeability of fluids, pore size and interconnection between pores It is very important that the pores of membrane produced by the nucleus-growth (NG) mechanism in the metastable region show closed pores, while the permeability of the membrane due to phase separation (SD) mechanism in the unstable region is not good. It has a high porosity and excellent permeability (SWSong et al., Journal of Membrane Science, 98 (1995) 209-222). By inducing to make it easy to position the film inside the pores have a cross-linked structure it is possible to improve the transmission performance. Therefore, when the non-solvent water or alcohol is added to the boundary of the binodal to the maximum to prepare a polymer solution to prepare a porous membrane, a membrane having improved permeability can be obtained. Relative humidity also affects pore growth. The higher the relative humidity, the higher the activity that can induce phase separation, and the faster the adsorption on the surface of the polymer solution acts as a mechanism to speed up the phase separation, and the overall decrease in the size of the pores, causing permeation decrease. Therefore, the mechanism for controlling the activity of water vapor under a constant relative humidity can be controlled by changing the composition of the polymer solution by the addition and content of non-solvent. A polyvinyl chloride membrane (JP 58-88011) prepared by using iso-propyl alcohol as a nonsolvent and controlling the structure of a nonwoven fabric has been reported, and a porous membrane is prepared by using a non-solvent of ethyl alcohol and using polyvinyl chloride. (JP 47-029266) The results have also been reported.

In the present invention, polyvinyl chloride is completely dissolved in tetrahydrofuran (THF), which is a solvent, and is well mixed with a solvent, and a mixed solution is prepared by adding an alcohol which acts as a non-solvent for a polymer, and then, a nonwoven fabric After impregnation and coating, the final membrane is prepared by inducing phase separation of the polymer under an atmosphere of 25 ° C. and 50-90% relative humidity. At this time, the choice of additives added in the polymer solution is limited because of the limitation of thermodynamic properties depending on the solvent and the type of polymer used. Since the added alcohol acts as a non-solvent, it increases the entanglement of the polymer chains, so that separation easily occurs in the high and low polymer concentration regions. At this time, these two regions are aggregated in order to lower their own surface tension, forming a skeleton of the formed membrane in the region of high polymer concentration, and the regions of low concentration grow into pores inside the membrane. Therefore, by controlling the content of the non-solvent additive, it is possible to control the physical entanglement of the polymer chain in the polymer solution in the region where phase separation does not occur, and the phenomenon is more pronounced in the solution to which the non-solvent having a relatively high boiling point is added. The present invention has been found.

As described above, when the porous membrane is manufactured according to the drying method under a constant humidity of the non-solvent-added polymer solution, the pore size is controlled by smoothly controlling the dynamic and thermodynamic phase separation mechanism according to the boiling point of the added non-solvent. It is also possible to obtain a membrane having a porous structure with high porosity.

Thus, the present invention forms a polymer solution by adding 1-40% by weight of alcohol, which is well mixed with a solvent and acts as a non-solvent for a polymer, to a solution in which polyvinyl chloride is dissolved in tetrahydrofuran (THF), In the method for producing a microporous polyvinyl chloride membrane and the method for producing the microporous membrane, the polymer solution is impregnated and applied to a polyester nonwoven fabric and then dried under an atmosphere of 25 ° C. and a relative humidity of 50-90%. By selecting an additive that has a boiling point of 50-150 ° C. and acts as a non-solvent for the polymer, the microporous polyvinyl chloride polymer membrane has a pore size of 0.01-2 μm and a porosity of 25-88%. It relates to a polyvinyl chloride polymer membrane, characterized in that the pure permeation flow rate of the porous polymer membrane is 25 to 7000LMH, The present invention relates to a porous polyvinyl chloride membrane having a method of preparing a microporous membrane and a pore size produced therefrom, and an improved flow rate of pure water, and a membrane prepared by the method according to the present invention has excellent permeability, and thus, Application is possible.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1-6

A mixed solution having a composition of 7 wt% polyvinyl chloride / 30 wt% nonsolvent (alcohol or water) / 63 wt% THF was prepared. After impregnating and applying this solution to a polyester nonwoven fabric, the phase separation was induced in an atmosphere of a temperature of 25 ° C. and a relative humidity of 60,70,80% to prepare a final membrane, and the pore size, porosity, and water permeability were measured. Is shown in Table 1.

TABLE 1

***: Value measured by electron scanning microscope observation with mean pore diameter

**: Pr (porosity) = (1- ρ _v / ρ _p ) × 100 ( ρ _v : polymer density at 25 ℃, ρ _p : membrane density)

*: Average value of pure water permeation amount (LMH: 1 / m ² hr)

Compared with the results of Comparative Example 1, it can be seen that the addition of 30% by weight of non-solvent increases the porosity and pore size, thereby improving the permeability of pure water. In addition, as the boiling point of the non-solvent used increased, permeability was generally improved.

Example 7-12

A mixed solution having a composition of 7 wt% polyvinyl chloride / 32 wt% nonsolvent (alcohol or water) / 61 wt% THF was prepared. After impregnating and applying this solution to a polyester nonwoven fabric, the resulting membranes were prepared by inducing phase separation under an atmosphere of a temperature of 25 ° C., a relative humidity of 60, 70, and 80%, respectively, to measure pore size, porosity, and water permeability. Is shown in Table 2.

TABLE 2

***: Value measured by electron scanning microscope observation with mean pore diameter

**: Pr (porosity) = (1- ρ _v / ρ _p ) × 100 ( ρ _v : polymer density at 25 ℃, ρ _p : membrane density)

*: Average value of pure water permeation amount (LMH: 1 / m ² hr)

As with the results of Example 1-6, it can be seen that the membrane prepared under conditions of high relative humidity while increasing the content of the non-solvent increases the pore size and porosity to increase the permeation rate of pure water. . Therefore, the porous membrane made of the non-solvent-added solution can improve the pore size and porosity by increasing the relative humidity.

Example 13-18

A mixed solution having a composition of 7 wt% polyvinyl chloride / 35 wt% nonsolvent (alcohol or water) / 58 wt% THF was prepared. After impregnating and applying this solution to a polyester nonwoven fabric, the resulting membrane was prepared by inducing phase separation under an atmosphere of temperature 25 ° C. and a relative humidity of 60, 70, 80% to measure pore size, porosity and water permeability. Table 3 shows.

TABLE 3

***: Value measured by electron scanning microscope observation with mean pore diameter

**: Pr (porosity) = (1- ρ _v / ρ _p ) × 100 ( ρ _v : polymer density at 25 ℃, ρ _p : membrane density)

*: Average value of pure water permeation amount (LMH: 1 / m ² hr)

As with the results of the previous Examples 1-12, the membrane prepared under the conditions of high relative humidity at the same time increasing the content of the non-solvent can be seen that the pore size and porosity of the membrane increases so that the permeation rate of pure water increases significantly. . However, when the additive is not added, as shown in the results in Comparative Examples 1-3, the relative humidity does not have a great influence on the porosity, and it can be seen that it acts as a factor for increasing the pore size. As a result, when the relative humidity is increased in the preparation of the non-solvent-free membrane, the pore size becomes slightly larger, but the porosity does not increase.However, when the non-solvent is added as an additive to the membrane manufacturing process, the relative humidity is greatly influenced by the porosity and As a major factor in the pore size, the permeability of pure water was improved. In particular, it can be seen that the boiling point shows the best permeability in Example 18, which is relatively high.

Comparative Example 1-3

7% by weight of polyvinyl chloride was completely dissolved in 93% by weight of THF to prepare a pure polymer solution without mixing of the non-solvent additive. After impregnating and applying the solution to the polyester nonwoven fabric, the resulting membranes were induced by inducing phase separation under a temperature of 25 ° C. and a relative humidity of 60, 70, and 80%, respectively, and pore size, porosity, and water permeability were measured. The results are shown in Table 4.

TABLE 4

***: Value measured by electron scanning microscope observation with mean pore diameter

**: Pr (porosity) = (1- ρ _v / ρ _p ) × 100 ( ρ _v : polymer density at 25 ℃, ρ _p : membrane density)

*: Average value of pure water permeation amount (LMH: 1 / m ² hr)

As can be seen from Table 4, the porosity of the membrane prepared as the relative humidity is increased in the polymer solution without the additive is not changed, but the pore size is slightly increased to increase the permeate flow rate. In other words, as the relative humidity increases, the pore size increases, which in turn promotes permeation of pure water.

As described above, in the present invention, a porous membrane can be obtained from a polyvinyl chloride solution containing a nonsolvent additive, and the pore size and porosity can be controlled by increasing the content of the nonsolvent and controlling the relative humidity. It is possible to manufacture a porous membrane having excellent permeability by increasing the interconnectability of the pores, which makes it possible to apply to microfiltration.

Claims (5)

After impregnating and applying a mixed solution composed of a polymer, a solvent, and an additive to a polyester nonwoven fabric, the polyvinyl chloride was dissolved in tetrahydrofuran (THF). 1-40% by weight of alcohol, which is well mixed with the solvent and acts as a non-solvent for the polymer, is added to form a polymer solution. The polymer solution is impregnated and applied to a polyester nonwoven fabric, and then the temperature is 25 ° C and a relative humidity of 50. Method for producing a microporous polyvinyl chloride membrane, characterized in that obtained by drying in -90% atmosphere The method of producing a microporous polyvinyl chloride membrane according to claim 1, wherein the non-solvent alcohol is any one selected from n-propyl alcohol and n-butyl alcohol. Microporous polyvinyl chloride membrane prepared by the method of any one of claims 1 to 2. 4. The microporous polyvinyl chloride membrane according to claim 3, wherein the pore size of the microporous polyvinyl chloride membrane is 0.01-2 占 퐉 and the porosity is 25-88%. 5. The microporous polyvinyl chloride membrane according to claim 4, wherein the pure permeation flow rate of the microporous polyvinyl chloride membrane is 25-7000 LMH.